This invention relates to fire and smoke dampers and more particularly to motorized dampers that are installed in air ducts, wall partitions, slot openings and the like and are designed to automatically close in the event of fire or extreme heat conditions.
Fire and smoke dampers have long been employed in ventilation, heating and air conditioning for the purpose of automatically closing the ductwork or an air passageway in the event of fire so as to prevent the spread of the fire and smoke through a building. Such automatic dampers generally comprise a curtain or shutter which is normally retained in an open position by a mechanical catch system which is automatically released when the temperature reaches a predetermined value.
Almost invariably, fire and smoke dampers have employed fusible links to effect automatic damper closure. For example, one known fire damper, shown in U.S. Pat. No. 4,161,204, has employed a fusible link in a cable that normally lifts a multifold curtain to a maintained open position. When there is a fire, the link fuses whereupon the cable separates into two portions and the raised curtain drops to close the damper. Unfortunately, once the fusible link melts, the damper is not automatically reopenable. The fusible link must be replaced, and the appurtenant cable repositioned before the curtain can be automatically lifted.